Field of the Invention
The invention relates to a method and process for thermal afterburning of oxidisable foreign bodies or impurities, fluid particles or gas contained in exhaust air from industrial working plants, such as drying chambers, in which plants there is produced a circulating air circuit flow which contains hot air serving to perform the respective operation within the industrial plant and which leaves the industrial plant carrying foreign substances or impurities, fluid particles or gas therewith, in which method and process a part of the circulating air is extracted from the circulating air circuit flow in the form of exhaust air and is introduced into a thermal afterburning plant, in which afterburning plant the foreign matter, the impurities, fluid particles or gas contained in, and carried by, the exhaust air are burned by supplying them energy, for example, by means of a burner arrangement. The invention relates also to a device for carrying out this new process and method. Such devices are used, for example, in connection with drying chambers, baking ovens, tempering furnaces, roasting furnaces, destilling plants, printing plants etc.
When carrying out known process of the kind here above described there must be supplied very much additional energy to the industrial working plant as well as to the afterburning plant, moreover it is also necessary to insulate very effectively and, therefore, very expensively the parts standing under the influence of high temperatures, especially the parts constituting the combustion chamber and, generally, the burning chamber arrangement. It is the aim of the present invention to avoid the above disadvantages.
For the above purpose there are provided according to the invention with the new process the following steps: to supply energy from outside of the general (industrial working plant and thermal afterburning plant) only to the afterburning working plant, whereby the exhaust air to be cleaned may be preheated more or less intensively within a heat exchanger arrangement and is burned afterwards within a combustion chamber, and to introduce the heat energy resulting during the combustion into the circulating air circuit flow directly by means of the hot cleaned exhaust gases or indirectly by means of a heat exchanger. A device for carrying out the new process is characterized by the fact that the afterburning plant is situated -- as seen in direction of flow -- downstream from the industrial plant and that it contains on the one hand a heat exchanger arrangement and on the other hand a burning chamber arrangement through which the exhaust air coming from the industrial plant is caused to flow after passing the heat exchanger arrangement and the outlet of which stands in connection with the circulating air circuit flow of the industrial working plant, wherein conveniently a branch conduit deviates from this connection to the circulating air circuit flow in a direction towards the chimney and wherein a fresh air conduit opens into this connection. However, the arrangement may also be such as to have the device contain a burning chamber arrangement through which on the one hand the exhaust air -- which leaves the industrial plant and the movement of which is assisted, for example, by means of a so-called circulating air blower -- is caused to flow and which on the other hand is passed around and cooled by the circulating air, and such as to have allotted to the burning chamber arrangement two heat exchanger arrangements of which the one is situated as seen in the direction of the flow of the circulating air downstream from the burning chamber arrangement and is passed through by the circulating air, whereas the other one is arranged as seen in direction of flow of the exhaust air upstream from the burning chamber arrangement and is passed through on the one hand by the exhaust air and on the other hand by the exhaust gases leaving the burning chamber arrangement. The arrangement may be, for example, also such that to the circulating air circuit flow of the industrial working plant and to the exhaust air flow to be afterburned there is allotted a commom heat exchanger arrangement which on the one hand lies within the circulating air circuit flow and on the other hand is passed through by the exhaust air. The exhaust air flow is thereby preheated within the heat exchanger portion allotted thereto and afterwards it is supplied to the burning chamber arrangement in order to be afterburned. The afterburned cleaned exhaust gases flow in the opposite direction again through this heat exchanger portion while transmitting due to the high gradient heat to the just arriving exhaust air flow in order to be cooled down at the same time. After this precooling operation the exhaust gases enter the heat exchanger allotted to the circulating air in order to perform here the heating of the circulating air. For direct heat transmission a partial flow of cleaned hot exhaust gases is supplied after having passed a part of the heat exchanger either to the burning chamber arrangement or directly to the circulating air. The remaining part of the flow reaches the chimney again under heat transmission through the heat exchanger.
The arrangement according to the invention distinguishes by the fact that substantially less energy is required since it is not necessary to supply energy on the one hand to the industrial plant and on the other hand to the afterburning working plant. The insulation may be simpler and less expensive, the parts of sheet metal are cooled by the circulating air so that material of lower and, therefore, less expensive quality may be used, whereby at the same time a higher service life and higher strength may be obtained. It is now possible to perform energy saving regulation operations under the highest burning chamber temperature since only a small amount of energy is transmitted to the circulating air in an uncontrollable manner and an exact regulation of the heat delivery and heat transmission within the heat exchanging arrangements is now possible. Generally speaking, the arrangement according to the invention is compact and requires less space, it is possible to build up a so-called compact unit which may contain the blower for the circulating air (conveniently a transverse flow blower), the burning chamber arrangement and the different heat exchanger arrangements, and also the different bypass arrangements, the blower for the exhaust air (for example, a transverse flow blower, too), etc.